Machining of metallic or other electrically conductive workpieces through electrical discharge machining is known to the prior art. Electrical discharge machining, sometimes hereinafter referred to as "EDM", is accomplished by electrical circuits which typically incorporate a number of electronic output switches that are operated to provide controllable duration machining power pulses across a dielectric coolant filled machining gap. Material is thus removed from the electrically conductive workpiece coincident with the gap dielectric breakdown each time a machining power pulse is passed across the gap. In order to insure predictability and repeatability of machining operation, the power supply circuit generally incorporates a pulsing means or a pulse generator which operates the electronic output switches, turning them on and off at precisely controllable frequencies and at controllable current magnitude. The use of solid state devices, such as transistors, as the electronic output switches is now common. One example of a power supply suitable for use with an electrical discharge machining apparatus is shown and described in Bell U.S. Pat. No. 3,737,615 for "Current and Frequency Control System for Electrical Discharge Machining Apparatus", which is of common ownership herewith.
The electrical discharge machining art has been extended to cover electrical discharge machining of a workpiece through a wire electrode in a known process in which the wire is fed continuously from a supply spool relative to the workpiece, with the electrical discharge machining pulses applied across the gap existing between the workpiece and the wire electrode in the above described manner. This type of electrical discharge machining has enabled the machining of minute and intricate patterns in workpieces with an efficiency and accuracy not known to other metal machining systems. In the more generally used wire electrode electrical discharge machining setups, the workpiece is attached to a table which is positioned in the X and Y axis directions through the operation of incrementally operated electrical motors so that the exact pattern of the cut made in the workpiece may be precisely controlled, for example, through numerical control units used in conjunction with the precision table. One example of this type of wire cutting arrangement is shown in my U.S. patent application Ser. No. 532,200, filed on Dec. 12, 1974, for "Wire Electrode Feed System for Electrical Discharge Machining", which application is of common ownership herewith.
It is important that the wire electrode apparatus and the control system used to position it relative to the workpiece should have the capability of cutting in other than strictly vertical directions through the workpiece. In many EDM work applications, it is important that the workpiece being produced, especially where it is to be used as a die, should have a relief provided. Thus, the capability in the machine tool apparatus of providing this relief, may eliminate any additional machining steps to effect the relief after the workpiece has been cut into the basic die shape. Other arrangements for accomplishing this general purpose, but of less efficient and more complicated nature, are shown, for example, in U.S. Pat. No. 3,849,624 issued to David H. Dulebohn et al for "Wire Electrode Electric Erosion Device".